The invention relates to the grinding of plane, annular surfaces. In particular, it is intended for the grinding of faying rings in gate valves, i.e. valves to be inserted in pipelines, in which two opposed inclined valve seats are equipped with metallic faying rings cooperating with corresponding rings on a wedge-shaped valve gate carried by a rod axially guided in the cover of an upwardly extending socket on the valve housing. In order to afford satisfactory sealing against operation pressures, the cooperating plane faces of the faying rings must be lapped at intervals, and since this is a heavy and time-consuming work, various types of grinding apparatus have been developed for the purpose. A difficulty in that connection is that the rings in the fixed valve housing are poorly accessible and the grinding apparatus must be operated and driven from outside the valve housing, and that the angle between the faying planes may vary from one manufacture to the other, even though there exist certain standard measures for the dimensions of the opening.
The apparatus mostly used for the purpose has been described in U.S. Pat. No. 2,720,736 and is equipped with a grinding disk which through bevel gears is driven for rotation by a shaft supported in a sleeve adjustably mounted in a fixed frame and is carried by a spherical head so as to be capable of adapting itself to varying angles of the faying surfaces and also to oblique positions of the supporting shaft of the disk relative to these.
Besides being complicated and expensive like other apparatus based on the same principle and described for example in Norwegian Patent specification No. 84 764 and French Patent specification No. 1 181 397, the apparatus disclosed in the said U.S. specification suffers from the serious drawback that the rotating grinding disks cut grooves in the faying faces and their own grinding faces are rapidly worn locally by these.
For remedying this drawbrack, some proposals have been published which, however, suffer from other important disadvantages and have had no success in practice.
Thus, the published German Patent application No. 2 400 077 shows a structure in which an arm rotating in a plane parallel to the annular surface carries a grinding head supported for rotation in the arm and driven by a turbine which is mounted in the arm and has an air supply thereto through a hose or centrally from the axis of rotation, or by a separate driving belt. Here the work is time-consuming, the design is complicated, especially as regards power supply, and above all it requires a extremely exact adaptation of the position of the arm relative to the annular surface, since there does not exist any self-adjusting effect like in the prior apparatus mentioned above.
Further, the U.S. Pat. No. 2,942,388 discloses various embodiments of grinding apparatus for the purpose, in which a grinding disk in addition to a rotational movement also performs a superposed reciprocating movement along the annular face. Here a self-adaptation is possible, but in return the design is extremely complicated and delicate.